Bulk shipping may generally be classified into several types based on the material being transported. For instance, pelletized material (such as bulk polymer) or mined material (such as coal) may be carried by a hopper car that allows for quickly depositing its payload into a receptacle. Such hopper cars are unsuitable for carrying dry cargo such as palletized loads which are generally shipped via trailer or dry container having a generally rectangular shape and compartment. Either is unsuitable for the third major category of material, specifically liquid.
The term intermodal transport as used herein refers to transporting bulk loads stored or loaded in containers without unloading the container. For instance, a container may be filled with loaded pallets, transported from a first site via over-land truck and container chassis, and then loaded onto a ship or railcar for further transport, likely subsequently loaded onto a second delivery truck and container chassis for delivery to its final destination. Throughout, the materials in the container remained loaded.
Intermodal transport standards are maintained by the International Standards Organization (ISO). Intermodal transport has received various contributions from around the world, including the United Kingdom, Canada, and the United States, and the ISO standards evolved from US Department of Defense standardization for military use.
Since about 1984 a form of intermodal transport known as “double-stack rail transport” has been used. As its name implies, this form only applies to rail transport, and this form involves stacking one container on top of another. The rail car itself is a either a flat car or a well car (that is, a railcar having a “well”) for partially receiving a bottom container therein.
For dry good transport, these stackable containers are the most common form of intermodal transport, though they need not always be stacked. The stackable containers are typically 8′ or 8′6″ wide, by 8′, 8′6″, or 9′6″ high, with a length of 20′, 40′, 48′, or 53′, though other heights have been considered. A container 9′6″ inches in height is commonly referred to as a “high cube” container and may be double stacked for total height of 19′, which is generally the maximum permitted under applicable legal restrictions. Each container is provided with support points, and the location of the support points is standardized so weight is properly transferred through the stacked containers. For instance, a 53-foot container may be placed on top of a pair of 20-foot containers, the top container having supports 40 feet apart aligned with the outer corners of the bottom containers.
Liquid transport requires a tank container that differs from dry goods containers for obvious reasons. The approach for intermodal tank containers has been to size the tank within a frame that mimics the construction of the dry goods container. To be specific, the overall dimensions of tank containers have been made to conform to those of dry goods containers. A typical tank container includes a frame surrounding the actual tank or vessel. The frame is eight feet by eight feet, six inches, and provides the container with an overall length of 20 feet, the tank container thus being sized essentially the same as a 20-foot dry goods container including support points. One benefit of a tank container having these dimensions is that it allows the tank container to be used on an intermodal rail car and in combination with dry goods containers. In other words, intermodal tank container development began with mimicking the dry goods container primarily for international transport, and everything else related to these tank containers grew from there.
This developmental mentality has produced a number of detriments, many of which are direct products of these design constraints. With respect to total costs, it is important in bulk shipping that little available payload is wasted on a per run basis. The tank within the frame is sized to maximize the space available, and a typical prior art tank container 20 feet in length carries a maximum of 26,000 liters with a product payload weight of 48,000 pounds or less due to US federal highway gross weight restrictions, bridge laws, and axle load restrictions, collectively referred to herein as the applicable legal restrictions. In greater detail, a gross vehicle weight is not permitted to exceed 80,000 pounds, which includes the tractor, the payload, and either the chassis and container or the integrated non-intermodal trailer.
While such tank container is generally matched in overall dimension to the shortest size of dry goods containers, the weight still exceeds that of the largest dry goods containers which are limited by the applicable legal restrictions. In order to accommodate such tank container on over-land truck use, a chassis is provided that is significantly different from that employed for dry goods use.
A chassis for dry goods use, along with a container thereon, gives a casual observer the impression of a typical semi tractor-trailer arrangement. One would see a semi tractor with a driver's cab, a chassis with the container thereon that looks like a typical non-intermodal trailer, and a fifth wheel hitch connecting the two. The overall height, width, and length of the chassis and container are substantially similar to that of the non-intermodal trailer. The intermodal dry goods container is lowered and secured onto the chassis after removal from a ship, or a railcar, or another truck, etc., transported to another location, and then removed from the chassis, while the standard trailer is loaded and unloaded at each point (often being laden with palletized loads).
In considering the chassis for a prior art intermodal tank container, the two things that should be recognized are the container's laden weight, both in relative terms to a laden dry goods container and in gross terms, and the overall shape of the tank. As discussed above, the loaded tank container is much heavier than a loaded dry goods container, and the chassis for a dry goods container is designed only to accommodate the weight of the dry goods container. At only 20 feet in length versus a 40-foot dry goods container, the greater weight of the loaded tank container is over a smaller length. Accordingly, a chassis for a tank container is specially designed for these physical characteristics.
A tank chassis is commonly referred to as a gooseneck, drop-deck chassis due to its shape and lower deck height. Longitudinally extending supports or beams span between a rear wheel assembly and the hitch connection. Because the weight of the tank container is concentrated over the 20 foot span of the container, these beams are much larger and stronger than for a dry goods chassis. The gooseneck shape and drop deck feature are results of the transported material being liquid: liquid moves around during transport, and this weight shifting combines with effects from being elevated to produce lateral forces that threaten rolling of the tank and chassis. The gooseneck and drop deck features lower the center of gravity of the tank container and, hence, the combination of the tank container and chassis to make the combined load more stable. In fact, the bulk of the weight of the beams is positioned between the rear wheel assembly of the chassis and a rear wheel assembly of the semi tractor, below the hitch connection.
While providing the tank container with the minimal overall dimensions of the smallest dry goods container, the resulting 20 foot tank container is nonetheless heavier than a 40 or 53 foot dry goods container, requiring a purpose specific chassis to be utilized. While a tank container chassis is much more expensive to build, it is unsuitable for use with dry goods containers (other than 20 foot dry goods containers).
As noted above, the gross vehicle weight is restricted by the applicable legal restrictions to 80,000 pounds. For a prior art intermodal container tank container and its accompanying tractor and chassis, the weight of the payload is generally in the range of 46,000 pounds to 48,000 pounds, which is partly restricted by the weight of the heavy gooseneck, drop-deck chassis required. For non-intermodal trailers, a similar range of payload weight is also achieved, largely due to the requirement of the larger tractor/sleeper necessary for OTR applications.
For prior art intermodal tank chassis, a special type of suspension is generally required, known as a spread axle rear tandem suspension that meets the US applicable legal restrictions. Under the gross vehicle weight restrictions, the 80,000 pounds is allotted to 12,000 pounds over the tractor front axles, 34,000 over the tractor rear axles (i.e., proximate the hitch connection), and 34,000 over the trailer/chassis rear axle pair. However, the prior art intermodal tank and chassis concentrates too much weight at the tractor rear axles. There is an exception to the 34,000 pounds on the rear axle for the spread axle rear tandem set up: by shifting the front axle of the two axles of the chassis rear pair to a 9′1″ spread (as opposed to the typical 49″ spread), one is permitted to have up to 39,000 pounds on this pair, as the weight is distributed over a greater area.
The spread axle rear tandem suspension is virtually required for an intermodal tank chassis. However, these systems are heavier, more expensive to operate, cause excessive tire wear, and are less maneuverable than a standard closed tandem suspension.
It should also be noted that, generally speaking, containers less than 40 feet present issues for stacking in rail cars. A pair of 20 foot containers are not stacked on top of a 40 or 53 foot container. The larger container does not have intermediate support points for the interior ends of the shorter containers. So, 20 foot containers (including all prior art intermodal tank containers) need to be either on the bottom of a stacked arrangement or on top of another 20 foot container. For this reason, the need to transport a single or odd number of 20 foot containers results in wasted rail capacity.
Accordingly, there has been a need for an improved intermodal tank container, an improved chassis for intermodal tank containers, and related components and methods for using intermodal tank containers.